Synthesis, Coordination Study, and Catalytic Pauson-Khand Reactions of QuinoxP*(CO)4-μ-Alkyne Dicobalt Complexes

Article abstract of DOI:10.1021/acs.organomet.7b00018

The coordination of the P-stereogenic and sterically demanding bisphosphine QuinoxP* to μ-alkyne dicobalt hexacarbonyl complexes was studied experimentally and computationally. Whereas the coordination occurred exclusively in a chelating fashion, the diastereoselectivity was highly substrate dependent. However, it could be explained from the computed structure and energies of the different coordination modes. The fluxional behavior of these complexes was also studied computationally. Their performance as catalysts for the Pauson-Khand reaction was explored, and outstanding reactivity was observed. Although the asymmetric induction was low to moderate, the stereochemical outcome could be mechanistically rationalized. This report provides promising results in terms of reactivity and mechanistic understanding for further developments of highly active chiral catalysts for intermolecular Pauson-Khand reactions.

Full text of DOI:10.1021/acs.organomet.7b00018

Article
pubs.acs.org/Organometallics
Synthesis, Coordination Study, and Catalytic Pauson−Khand
Reactions of QuinoxP*(CO)4‑μ-Alkyne Dicobalt Complexes
Martí Garco̧
n,† Albert Cabre,† Xavier Verdaguer,*,†,‡ and Antoni Riera*,†,‡
́
†Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac 10,
Barcelona E-08028, Spain
‡Departament de Química Inorgan
̀ ̀ ́ ̀ ̀
ica i Organica, Seccio Organica. Universitat de Barcelona, Martí i Franques 1, Barcelona E-08028,
Spain
S
* Supporting Information
ABSTRACT: The coordination of the P-stereogenic and
sterically demanding bisphosphine QuinoxP* to μ-alkyne
dicobalt hexacarbonyl complexes was studied experimentally
and computationally. Whereas the coordination occurred
exclusively in a chelating fashion, the diastereoselectivity was
highly substrate dependent. However, it could be explained from
the computed structure and energies of the different coordina-
tion modes. The fluxional behavior of these complexes was also
studied computationally. Their performance as catalysts for the
Pauson−Khand reaction was explored, and outstanding reactivity
was observed. Although the asymmetric induction was low to
moderate, the stereochemical outcome could be mechanistically rationalized. This report provides promising results in terms of
reactivity and mechanistic understanding for further developments of highly active chiral catalysts for intermolecular Pauson−
Khand reactions.
INTRODUCTION
■
Dicobalt octacarbonyl is one of the most popular dinuclear
complexes bearing a metal−metal bond, which has been used in
a wide range of carbonylative1 and noncarbonylative processes.2
Particularly, μ-alkyne dicobalt hexacarbonyl complexes have
found many uses, including applications in polymer science3
and biomedicine.4 Furthermore, they have become invaluable
tools in organic synthesis, as alkyne protecting groups (or
stabilizing groups for strained cycloalkynes),5 or as key
components in [2 + 2 + 2] cycloadditions,6 Nicholas reactions,7
and Pauson−Khand reactions (PKRs).8,9
Their structure consists of a tetrahedral core,10 in which the
alkyne coordinates to both cobalt atoms in a μ-η2:η2 fashion
and the remaining CO ligands complete the coordination
spheres, in such a way that these complexes belong to the C2v
symmetry point group, when the alkyne is symmetrically
substituted. If the alkyne is not symmetrical, the C2 axis is then
lost and the two homotopic cobalt atoms become enantiotopic.
Several efforts have been devoted to the desymmetrization of
these alkyne dicobalt clusters by using chiral ligands or reagents
for applications in asymmetric synthesis.11 Although the
substitution of CO’s by chiral ligands can give rise to multiple
coordination modes, this number is normally reduced to one or
two diastereomers due to fluxional processes which inter-
convert equatorial (eq) and axial (ax) positions within a cobalt
atom (Figure 1).12
Figure 1. Nomenclature of the different CO positions (supposing that
R has higher priority than R′) and formation of stereoisomeric alkyne
dicobalt complexes when introducing a chiral monodentate ligand
(L*).
κ1:κ1) fashion.13 For unsymmetrical alkynes there could be up
to 4 bridged and 12 chelated possible diastereomers that would
be reduced to 2 bridged and 6 chelated isomers using C2-
symmetric ligands.14 However, in most cases due to selectivity
and fluxionality, the number of diastereomers is reduced to only
2.
The coordination mode of bidentate ligands is actually
crucial in the reactivity of the complexes. Furthermore, their
Bidentate ligands can bind to the same cobalt atom in a
Received: January 11, 2017
chelated (κ2) fashion or to both cobalt atoms in a bridged (μ-
© XXXX American Chemical Society
A
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properties and stability can also vary significantly. An illustrative
example are the BINAP-(μ-alkyne)dicobalt carbonyl complexes
reported independently by Laschat15 and Gibson.16 From tert-
butylacetylene only a bridged isomer was obtained, whereas for
less hindered alkynes (such as acetylene, phenylacetylene, and
methyl propiolate) and enynes chelated isomers are selectively
formed. Remarkably, the reactivity of the bridged BINAP-
(μ-tBuCCH)-Co2(CO)4 complex in the Pauson−Khand
reaction is practically nonexistent, whereas for the chelated
examples the reaction occurs in moderate yields.
Although several efficient systems have been developed for
the asymmetric intramolecular reaction,14b,17 the intermolecular
PKR has proven to be much more challenging. In general, the
poor reactivity of bisphosphine complexes in the Pauson−
Khand reaction is one of the principal reasons for the scarce
presence of these complexes in the literature, with only few
examples that show significant activity in the intermolecular
PKR14a,18 using electron-poor bisphosphines.
was performed. No reaction was observed at room temper-
ature; thus, higher temperatures were required. The optimal
conditions found were heating at 70 °C for 5 h (in some
substrates longer reaction times are not detrimental) and
purging the system (with N2 or vacuum cycles) every ca. 30
min, to avoid CO overpressure and facilitate the substitution.
However, total elimination of the CO (i.e., under constant N2
flow) destabilizes the complexes. Working on a small scale and
filtering the starting hexacarbonyl complex through a silica plug
immediately before the reaction usually provides the best yields
(Table 1). These complexes are relatively unstable, producing
small amounts of paramagnetic cobalt that hinder their
characterization by NMR (see Figure S1 in the Supporting
Information).
Table 1. Preparation (under Optimized Conditions) of
QuinoxP*-μ-alkyne-Co2(CO)4 Complexes
Our group has developed several chiral bidentate bridging
hemilabile (P,S) ligands which gave outstanding results in
terms of enantioselectivity in the intermolecular PKR.19
However, the Co complexes of these ligands had to be used
stoichiometrically, since they gave poor enantioselectivities in
the catalytic version of the reaction.20
a
entry
starting complex
product, yield (%) diastereomeric ratio
1
2
3
4
5
2a (R = H)
3a, 36
Very recently our group reported the first Co-catalyzed
example with good yields and useful levels of enantioselectivity
using the novel bisphosphine ThaxPHOS.18 The range of
alkynes, however, was limited to silylacetylenes. These inspiring
results in terms of activity and enantioselectivity prompted us
to study other bisphosphine cobalt complexes in order to
deeply understand the behavior of these complexes. This would
ultimately enable us to design proficient and more general
chiral catalysts for the catalytic and intermolecular PKR.
We decided to use the bulky P-stereogenic C2-symmetric
ligand QuinoxP*, developed by Imamoto and co-workers,21 as
it has been proved to provide excellent results in a wide range
of asymmetric transformations.22 Furthermore, the proximity of
the chiral centers to the metal, the significant steric hindrance,
and the relatively electron poor character given by the
quinoxaline ring, made QuinoxP* a promising ligand to
develop efficient PKR catalysts and an interesting case study
to analyze all these effects in μ-alkyne dicobalt complexes, as
well as to gain a deeper insight into these useful complexes.
Hence, we describe herein the synthesis, coordination study,
and catalytic activity of QuinoxP*(CO)4-μ-alkyne dicobalt
complexes.
2b (R = n-octyl)
2c (R = Ph)
3b, 45
3c, 70
3d, 33
3e, 46
1.3:1
4:1
2d (R = C(Me)2OH)
2e (R = TMS)
8:1
10:1
a
Measured by 31P NMR.
Characterization and Structural Analysis. All complexes
3 were fully characterized by conventional techniques (1H, 31P,
and 13C NMR, IR, and MS). In all cases, except for the
symmetric 3a, two diastereomers were observed by NMR
(Figure 2). Remarkably, for complex 3e or 3d with a TMS or
RESULTS AND DISCUSSION
■
Synthesis and Stability of QuinoxP* Complexes. As a
representative set of terminal alkynes, we selected acetylene
(1a), 1-decyne (1b), phenylacetylene (1c), 2-methylbut-3-yn-2-
ol (1d), and trimethylsilylacetylene (1e). The starting μ-alkyne
dicobalt hexacarbonyl complexes 2 were prepared by mixing
Co2(CO)8 with the corresponding alkynes in hexane. In the
case of (μ-HCCH)-Co2(CO)6, acetylene gas was bubbled into
a Co2(CO)8 solution. The complexes obtained can be purified
by filtration through silica to remove the remaining unreactive
cobalt decomposition to afford the pure desired complexes in
excellent yields (see Table S1 in the Supporting Information).
Once the hexacarbonyl complexes were prepared, QuinoxP*
complexes 3 were subsequently synthesized by ligand
substitution of two carbonyl ligands. The initial yields obtained
were low; therefore, a screening to find the optimal conditions
Figure 2. 31P NMR of QuinoxP* complexes 3a−e.
CMe2OH substituent, one diastereomer was greatly favored.
The selectivity decreased in the case of 3b (n-octyl) and 3c
(Ph). Apparently, the bulky substituents on the alkyne increase
the diastereoselectivity of the coordination.
Complex 3c showed a distinctive equilibration behavior.
When the reaction was performed with heating for 4 h, a ca. 1:1
mixture of diastereomers was obtained. However, if the mixture
was heated for 6−7 h, equilibration between the two
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Table 2. Computed Energies (ΔG) of All Possible Coordination Modes of (S,S)-QuinoxP* Dicobalt Complexes of Different
b
Alkynes (HCCR)
a
Cobalt atoms in complex 2a are homotopic. In this particular case, the pro-S/pro-R notation is inappropriate, but it was kept for the sake of
generalization with the other substrates. Thus, for 3a, chelated_pro-R (ax-eqtrans), chelated_pro-S (ax-eqtrans), and chelated_pro-R (eq-eq) are in fact
b
conformers that can be interconverted through turnstile rotation. Energies in kcal/mol are referenced to the most stable chelated trans
diastereomer.
diastereomers occurred to afford a ca. 3:1 diastereomeric
mixture. Heating overnight yields a ca. 4:1 mixture of
diastereomers, in which the major diastereomer is the one
whose X-ray structure was obtained (vide infra).
unlikely, since the fluxional processes would favor the trans over
the cis form. For these reasons, we hypothesized that the
coordination of QuinoxP* occurred exclusively via chelation.
In order to gain a deeper insight into these QuinoxP*
complexes, molecular orbital calculations were performed. The
geometries of the different bridged and chelated diastereomers
of QuinoxP* dicobalt complexes were optimized using density
functional theory (DFT) implemented in the Gaussian09
program package.23 The calculations were done using the
B3LYP functional and the standard 6-31+G(d,p) basis set. The
energies of all possible diastereomers of the cobalt complexes
3a−e are shown in Table 2.
For symmetrical alkynes such as acetylene, up to four
stereoisomers (one bridged and three chelated) are possible.
However, by fluxionality between the three chelated isomers
bound to the same cobalt atom (ax-eqcis, eqcis-eqtrans, and ax-
eqtrans) this number would be reduced to two: just one bridged
and one chelated isomer. In the case of the acetylene cobalt
In order to discern the coordination mode (bridged,
chelated, or a mixture of both), the NMR spectra gave little
information. Nonetheless, the alkyne proton appeared as a
doublet of doublets (dd) with coupling constants approx-
4
4
imately in the range JH−P = 6.5−8.5 Hz and JH−P = 1.8−3.8
Hz, respectively. This fact would be consistent with the
presence of chelated isomers, since the coupling constants with
an axial and an equatorial phosphorus would be significantly
different.
An FT-IR analysis was then performed, and we were pleased
to see that for all cases the CO stretching bands were practically
identical. The presence of a mixture of bridged and chelated
isomers was then discarded. In the case of complexes 3c and
3b, the possibility of two bridged diastereomers was considered
C
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complex 3a only one set of signals was observed by NMR (see
Figure 2). According to the calculations the most stable isomer
is an axial−equatorial chelated complex which is 11.4 kcal/mol
more stable than the bridged complex. Therefore, we assumed
that those signals correspond to the chelated complex.
For terminal alkynes, two bridged and six chelated complexes
were located. Gratifyingly, several trends could be observed.
First, the chelated ax-eqtrans diastereomers were always the most
stable (6−11 kcal/mol lower than the bridged isomer). This
can be explained taking into account the size of linker between
both phosphorus atoms. The coordination mode (bridged or
chelated) is crucially determined by this factor. For instance, for
one-atom linkers the coordination is exclusively bridged, since a
chelated coordination would afford a strained four-membered
ring.24 According to the present calculations, the linker with
two (planar carbon) atoms affords the chelated coordination
with the corresponding formation of a five-membered ring. The
formation of the bridged isomers is not favored because this
type of linker is too small to permit a geometrically unstrained
six-membered ring. For bigger linkers, as in the case of BINAP,
although the chelated isomer is normally favored, the linker also
allows nonstrained bridged coordination modes. For this
reason, for tert-butylacetylene complexes with BINAP the
bridged isomer is obtained,15 since this disposition minimizes
the steric clash of the ligand with the bulky tert-butyl group.
The chelated equatorial−equatorial isomers were found to be
3.5−7.9 kcal/mol less stable than the most stable axial−
equatorial stereoisomers. As could be expected for steric
reasons, the chelated ax-eqcis complexes were 1.5−5.1 kcal/mol
less stable than the trans species. Therefore, the two most stable
stereoisomers were the ax-eqtrans form chelated to either the pro-
R or the pro-S cobalt atom (Figure 3).
In the case of 3b a n-propyl chain was used as a model of the
n-octyl chain to reduce the computational cost. In this case
both ax-eqtrans stereoisomers were nearly equal in energy.
However, for 3c−e the difference increased to 1.2, 1.9, and 1.4
kcal mol−1, respectively, toward the complex with the S,S ligand
chelated to the pro-R cobalt atom (Table 2 and Figure 3).
Most gratifyingly, the X-ray diffraction of the major
diastereomer of complex 3c (Figure 4) showed a trans-axial−
equatorial chelated geometry in complete agreement with the
most stable calculated geometry. Moreover, the employed level
of theory accurately reproduced the experimental geometry,
since the difference in the key geometric parameters (bond
distances and angles) between the computed and the
experimental structures (X-ray) was less than 1% (Table S1
in the Supporting Information).
Figure 3. The two most stable computed structures for complex 3c
from (S,S)-QuinoxP*, corresponding to pro-S (1.2 kcal/mol) and pro-
R (0.0 kcal/mol) axial−equatorialtrans chelated diastereomers. Hydro-
gen atoms are omitted for clarity.
In summary, the calculations nicely reproduce the exper-
imental mixture of complexes observed by 31P NMR. For
complexes 3d,e, the difference between the two diastereomers
(ax-eqtrans diastereomers) is around 1.4−1.9 kcal/mol, and one
diastereomer is mainly observed. For 3c, with a difference of
around 1.2 kcal/mol, both diastereomers are formed, but
equilibration between them occurs to afford an enriched
mixture of the most stable diastereomer. Finally, for complex
3b (in the calculations the octyl chain has been replaced by a
propyl chain to avoid excessive computational cost) there is
practically no energetic difference between diastereomers, and
both are experimentally obtained and no equilibration is
observed. We can then conclude that there is a thermodynamic
control in the coordination of ligands to alkyne dicobalt
complexes. The equilibration observed for complex 3c, as well
as many other reported examples of this behavior,18−20 strongly
Figure 4. X-ray structure of the major diastereomer of complex 3c
from (S,S)-QuinoxP*: ORTEP drawing showing 50% probability
ellipsoids. The elucidated structure corresponds to the pro-R ax-eqtrans
chelated isomer.
support this conclusion, allowing DFT calculations to become a
useful predictive tool for the diastereoselectivity of the
coordination of chiral ligands to these complexes, by solely
computing the energies of the products (alkyne-Co2(CO)n-Ln
complexes). Nonetheless, it must be taken into account that in
this case the computed energetic differences are rather small,
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and although they are systematically consistent with the
experimental results, cannot be used in quantitative trends.
Fluxionality of QuinoxP* around a Single Cobalt
Center. For the symmetric complex 2a, derived from
acetylene, both cobalt centers are homotopic. Thus, coordina-
tion of (S,S)-QuinoxP* to either Co center provides a single
stereoisomer. However, coordination of the bisphosphine
ligand around the cobalt atom gives rise to three possible
diastereomeric conformers (eq-ax/ax-eq′/eq-eq′, Scheme 1).
Chart 1. Potential Energy Scan of the Turnstile Rotation of
Complex 3a for the Interconversion of Conformers, with
Respect to the Dihedral Angle (deg) P16−Co2−Co4−C3
a
Scheme 1. Fluxional Behavior for Complex 3a
a
Turnstile rotation interconverts three possible diastereomeric con-
formers.
While the 31P NMR spectrum of complex 3a showed a single
set of signals corresponding to each diastereotopic phosphorus
atom (see Supporting Information), calculations suggested that
the eq-ax/ax-eq′ conformers were almost equal in energy
(Table 2). These results implied that there had to be low-
energy fluxional pathways which interconverted both con-
formers.
With the aim of studying more in detail the fluxional
processes occurring in chelated bisphosphine-(CO)4-μ-alkyne
dicobalt complexes, we decided to perform a computational
search for the barriers of turnstile rotation in complex 3a. A
scan of the potential energy surface of rotation was performed,
and as expected, single barriers between conformers were
observed. The barrier between the ax-eq′/eq-eq′ and eq-ax/eq-
eq′ conformers was higher (around 11 kcal/mol) than the
barrier between ax-eq′/eq-ax conformers. Thus, there is a low-
energy pathway of direct interconversion between ax-eq′ and
eq-ax diastereomeric conformers. Nevertheless, the longer
interconversion pathway with two barriers going through the
eq-eq′ intermediate is not excessively disfavored; therefore, at
room temperature complete turnstile rotation should occur
(Chart 1).
In order to better characterize the fluxional process, the
lowest energy transition state (TS1) between eq-ax/ax-eq′
conformers was specifically computed, showing it to be 9.2
kcal/mol higher in energy than the lowest energy conformer. It
should be highlighted that the computed potential energy is
very similar to the value obtained for the dihedral angle scan.
While for the three minima the cobalt atom bearing the
bisphosphine ligand has a pseudo-octahedral geometry, for TS1
it adopts a pseudo-trigonal-prismatic geometry (Figure 5). For
the sake of comparison, the turnstile rotation of the three CO
ligands attached to the other cobalt atom of complex 3a was
also examined. The potential energy barrier obtained (in the
scan analysis) was just around 3 kcal/mol, which implies
Figure 5. Computed structure for TS1, resulting from turnstile
rotation of QuinoxP* in complex 3a.
extremely fast rotation. Logically, the rotation of QuinoxP* is
slower, but it is fast enough to experimentally observe a single
set of signals for complex 3a.
Catalytic Performance. Cobalt QuinoxP* complexes 3
were then evaluated as catalysts for the intermolecular Pauson−
Khand reaction of alkynes 1b−j. Since after the first catalytic
cycle all catalysts should perform the same way, we used 3a,c as
catalysts for practical reasons. In this way, the yield obtained is
truly from the catalytic reaction, since the first cycle affords a
different adduct. The results are summarized in Table 3. Except
for the more hindered alkynes (1d,e,h), we were delighted to
observe that our catalysts were highly active PKR catalysts. In
general, the desired products were obtained in excellent yields
and purity with 3−7% mol catalyst loading. The lack of
reactivity of more hindered alkynes could be attributed to
excessive steric encumbrance of the ligand and the bulky TMS
or −C(Me)2OH groups. In the case of propargyl acetate (see
entry 6, Table 3) a remarkable 40% yield was obtained. It
should be noted that this is a difficult substrate for PKR since
the stoichiometric PKR under either thermal or NMO
activation gives very poor yields. For the more demanding
internal alkyne (see entry 9, Table 3), the reaction rate is slower
but the yield after 16 h is also good. Thus, we can conclude that
QuinoxP*-Co2 complexes are highly active catalysts in the
intermolecular Pauson−Khand reaction of nonbulky alkynes.
The steric hindrance imparted by the ligand seems to boost the
PKR yields, except for very hindered alkynes. In those cases, the
excessive hindrance proved to be deleterious.
E
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a
Table 3. Enantioselective Catalytic Pauson−Khand Reactions
catalyst, catalyst loading
product, yield
(%)
entry
alkyne
(mol %)
chirality of the ligand reaction conditions
ee (%)
[α]D
1
2
3
4
5
6
7
8
9
1b (R = n-octyl, R′ = H)
1c (R = Ph, R′ = H)
1e (R = TMS, R′ = H)
1d (R = C(Me)2OH, R′ = H)
1f (R = CH2OTBS, R′ = H)
1g (R = CH2OAc, R′ = H)
1h, (R = CH(Me)OH, R′ = H)
1i (R = cyclopropyl, R′ = H)
1j (R = Ph, R′ = Ph)
3c, 5
3c, 3
3e, 4
3c, 5
3a, 7
3c, 5
3c, 7
3a, 5
3c, 7
S,S
S,S
S,S
S,S
R,R
S,S
S,S
S,S
S,S
overnight at 95 °C
overnight at 100 °C
overnight at 120 °C
overnight at 110 °C
6 h at 100 °C
overnight at 100 °C
overnight at 100 °C
overnight at 110 °C
overnight at 120 °C
4b, 99
4c, 94
4e, 12
4d, 16
4f, 86
4g, 40
34−41
<5
<5
25
8
+
+
5
b
4h, 22
30
43
15
+
+
+
4i, 99
c
4j, 54
a
b
c
The CO pressure was set to 1.5 barG. Obtained as a ca. 2:1 mixture of diastereomers. 54% yield with 56% conversion.
The enantioselectivity of the reactions was then analyzed by
configuration of the final adduct.12 We needed to assume that
anti cobaltacycles are significantly more stable than the syn
species, which is supported by calculations.26 According to this
scheme, coordination of the olefin to the pro-S cobalt atom
would lead to the (+)-IV adduct, whereas coordination to the
pro-R atom would afford its enantiomer. According to our
calculations (Table 2) starting from (S,S)-QuinoxP* the most
stable diastereomer is that in which the ligand coordinates to
the pro-R cobalt atom. Therefore, the olefin should coordinate
to the pro-S Co leading to the dextrorotatory isomer (+)-IV as
experimentally observed.
chiral HPLC (Table 3). Although the enantiomeric excesses
obtained were low to moderate, it is noteworthy that for 1-
decyne (1b, entry 1, Table 3) and cyclopropylacetylene (1i,
entry 8, Table 3) the asymmetric induction was significant,
these results being the best enantioselectivities reported to date
for substrates with alkyl chains.18
For all cases in which the induction was significant, the
optical rotation was observed to be dextrorotatory (+) when
(S,S)-QuinoxP* was employed. Since the substituent of the
alkyne has little effect on the optical rotation of these PK
adducts, we assigned the absolute configuration of these
adducts to be (+)-(S,S,S,R)-IV, as shown in Scheme 2.13
The stereochemical outcome observed can be rationalized by
taking into account the accepted mechanism for the
intermolecular PKR,25 as well as the stereochemical pathway
that links the coordination of the olefin to the absolute
CONCLUSIONS
■
Imamoto’s P-stereogenic and bulky bisphosphine ligand
QuinoxP* was employed successfully in the preparation of μ-
alkyne-Co2(CO)4(QuinoxP*) complexes. Their chelated coor-
dination mode was disclosed both experimentally and
computationally, and its turnstile fluxionality has been studied
by theoretical calculations. Their activity as PKR catalysts has
also been investigated, and remarkable reactivity has been
observed. Although the asymmetric induction is still not
synthetically useful, the good reactivity and mechanistic insight
of this report will help in the future development of new
efficient chiral catalysts for the catalytic, intermolecular
Pauson−Khand reaction.
Scheme 2. Stereochemical Pathway from the Most Stable
Diastereomer of (S,S)-QuinoxP* Complex to the
a
Dextrorotatory PK Adduct
EXPERIMENTAL SECTION
■
Computational Considerations. The geometries of the products
were optimized using the B3LYP hybrid exchange-correlation
functional with the Gaussian09 program suite. Stationary points
were characterized depending on their imaginary frequencies (1 and 0
for TSs and minima, respectively). The split-valence 6-31+G(d,p)
basis set was employed. The solvent effects were not taken into
account, since the reactions were carried out in rather nonpolar
solvents.
Experimental Procedures and Characterizations. (R,R)-
QuinoxP*-Co2(CO)4-(μ-HCCH) (3a). Freshly filtered (through a silica
plug) acetylene dicobalt hexacarbonyl complex 2a (60 mg, 0.19 mmol,
1.1 equiv) was dissolved in anhydrous toluene (1.5 mL). A solution of
(R,R)-QuinoxP* (60 mg, 0.18 mmol, 1 equiv) in anhydrous toluene (3
mL) was then added dropwise. The resulting mixture was stirred at 70
°C for 4 h. The system was purged with vacuum/N2 cycles every 5 min
for 30 min, then every 10 min for 1 h, and finally every 30 min for 2.5
h. The crude product was then filtered through an alumina plug, and
a
The stereochemically irrelevant steps of CO insertion and reductive
elimination are included (in brackets) for mechanistic completeness
and clarity.
F
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the product was purified by column chromatography in neutral
140.6 (s, C), 141.6 (s, C), 143.3 (s, C), 203.8 (s, 4 × C). IR (ATR) ν
(cm−1): 3063, 3015, 2958, 2920, 2901, 2863, 2031, 1963, 1473, 1215,
883, 751. HRMS (ESI): calcd for [C29H34Co2N2O3P2]+ 638.0703,
found 638.0699 [M − CO]+. Asterisks denote signals corresponding
to a diastereomer.
alumina using hexane/EtOAc (from 100/0 to 90/10) as the eluent to
1
afford 3a (38 mg, 36% yield) as a dark red oil. H NMR (500 MHz,
CDCl3): δ (ppm) 1.06 (d, 3JH−P = 14.3 Hz, 9H), 1.17 (d, 3JH−P = 14.6
2
2
Hz, 9H), 1.76 (d, JH−P = 7.6 Hz, 3H), 1.93 (d, JH−P = 7.0 Hz, 3H),
5.18−5.24 (m, 2H), 7.84−7.90 (m, 2H), 8.15−8.21 (m, 2H). 31P{1H}
NMR (202 MHz, CDCl3): δ (ppm) 54.41, 60.81. 13C NMR (126
MHz, CDCl3): δ (ppm) 11.3−12.2 (m, 2 × CH3), 27.0 (s, 6 × CH3),
(R,R)-QuinoxP*-Co2(CO)4-(μ-HCCC(Me2)OH) (3d). 2-Methyl-3-
butyn-2-ol dicobalt hexacarbonyl complex 2d (98 mg, 0.26 mmol, 1
equiv) was dissolved in anhydrous toluene (5 mL). A solution of
(R,R)-QuinoxP* (90 mg, 0.26 mmol, 1 equiv) in anhydrous toluene (2
mL) was then added dropwise. The resulting mixture was stirred at 80
°C overnight with a gas outlet. The crude mixture was filtered through
an alumina plug, and the product was purified by column
chromatography using hexane/EtOAc (from 100/0 to 50/50) as the
eluent to afford 3d (56 mg, 33% yield) as a dark red oil. 1H NMR (400
MHz, CD3CN): δ (ppm) 0.93 (d, 3JH−P = 14.3 Hz, 9H), 1.16 (d, 3JH−P
1
1
34.1 (d, JC−P = 19.9 Hz, C), 35.2 (d, JC−P = 16.7 Hz, C), 70.2 (d,
3JC−P = 6.5 Hz, CH), 71.7 (d, JC−P = 9.5 Hz, CH), 130.2 (d, JC−P
=
2
4
7.9 Hz, 2 × CH), 131.6 (d, 5JC−P = 6.1 Hz, 2 × CH), 140.9 (d, 3JC−P
=
3
5.9 Hz, C), 141.2 (d, JC−P = 5.4 Hz, C), 160.5−162.5 (m, 2 × C),
204.9−207.0 (m, 3 × C), 208.1−209.7 (m, C). IR (ATR) ν (cm−1):
2955, 2926, 2870, 2895, 2033, 1960, 1474, 886, 763. HRMS (ESI):
calcd for [C23H30Co2N2O3P2]+ 562.0390, found 562.0404 [M −
CO]+.
2
= 14.1 Hz, 9H), 1.60 (s, 3H), 1.64 (s, 3H), 1.87 (d, JH−P = 7.7 Hz,
3H), 1.88 (d, 2JH−P = 7.6 Hz, 3H), 2.54 (s, 1H), 5.48 (dd, 4JH−P = 6.6
(S,S)-QuinoxP*-Co2(CO)4-(μ-HCC(CH2)7CH3) (3b). 1-Decyne dico-
balt hexacarbonyl complex 2b (112 mg, 0.26 mmol, 1 equiv) was
dissolved in anhydrous toluene (5 mL). A solution of (S,S)-QuinoxP*
(90 mg, 0.26 mmol, 1 equiv) in anhydrous toluene (2 mL) was then
added dropwise. The resulting mixture was stirred at 80 °C overnight
with a gas outlet. The crude was filtered through an alumina plug and
the product was purified by column chromatography in silica gel using
hexane/EtOAc (from 100/0 to 90/10) as the eluent to afford 3b (as a
1/1 mixture of diastereomers) (82 mg, 45% yield) as a dark red oil. 1H
NMR (500 MHz, CDCl3): δ (ppm) 0.85−0.91 (m, 6H), 0.94 (d, 3JH−P
4
Hz, J′H−P = 3.8 Hz, 1H), 7.93−7.99 (m, 2H), 8.17−8.25 (m, 2H).
31P{1H} NMR (202 MHz, CD3CN): δ (ppm) 50.32, 63.76. 13C NMR
(126 MHz, CD3CN): δ (ppm) 11.4−12.1 (m, 2 × CH3), 27.6 (s, 3 ×
2
CH3), 27.9 (d, JC−P = 5.9 Hz, 3 × CH3), 32.4 (s, CH3), 34.8−34.9
(m, C), 35.0 (s, CH3), 36.1 (d, 1JC−P = 17.3 Hz, C), 70.5 (s, CH), 72.6
(s, C), 80.9 (s, C), 130.7 (d, 4JC−P = 10.6 Hz, 2 × CH), 132.9 (d, 5JC−P
= 15.8 Hz, 2 × CH), 141.4 (s, C), 141.9−143.1 (m, C), 163.0−164.3
(m, 2 × C), 204.9−205.9 (m, 4 × C). IR (ATR) ν (cm−1): 3370, 2958,
2926, 2898, 2866, 2054, 2026, 1963, 1173, 889. HRMS (ESI): calcd
for [C27H36Co2N2O5P2 + H+] 649.0836, found 649.0832.
3
3
= 14.2 Hz, 9H), 1.01 (d, JH−P = 13.8 Hz, 9H), 1.13 (d, JH−P = 14.5
3
Hz, 9H), 1.13 (d, JH−P = 14.0 Hz, 9H), 1.21−1.42 (m, 20H), 1.44−
(S,S)-QuinoxP*-Co2(CO)4-(μ-HCCTMS) (3e). Trimethylsilylacety-
lene dicobalt hexacarbonyl complex 2e (101 mg, 0.26 mmol, 1
equiv) was dissolved in anhydrous toluene (5 mL). A solution of (S,S)-
QuinoxP* (90 mg, 0.26 mmol, 1 equiv) in anhydrous toluene (2 mL)
was then added dropwise. The resulting mixture was stirred at 70 °C
with a gas outlet for 4 h until completion (TLC monitoring). The
crude mixture was filtered through an alumina plug, and the product
was purified by column chromatography in silica gel using hexane/
EtOAc (from 100:0 to 80:20) as the eluent to afford 3e (80.6 mg, 46%
yield) as a dark red oil. 1H NMR (400 MHz, CDCl3): δ (ppm) 0.35 (s,
1.51 (m, 2H), 1.69 (d, 2JH−P = 7.9 Hz, 3H), 1.71−1.77 (m, 1H), 1.80−
1.86 (m, 6H), 1.87−1.96 (m, 1H), 2.01 (d, 2JH−P = 6.1 Hz, 3H), 2.67−
2.85 (m, 2H), 2.86−3.02 (m, 2H), 5.20 (d, 4JH−P = 12.5 Hz, 1H), 5.32
4
(d, JH−P = 8.1 Hz, 1H), 7.80−7.92 (m, 4H), 8.12−8.25 (m, 4H).
31P{1H} NMR (202 MHz, CDCl3): δ (ppm) 47.47, 52.40, 63.79,
67.46. 13C NMR (126 MHz, CDCl3): δ (ppm) 10.5 (d, JC−P = 16.5
1
1
1
Hz, CH3), 10.9 (d, JC−P = 14.4 Hz, CH3), 11.1 (d, JC−P = 6.5 Hz,
1
CH3), 11.8 (d, JC−P = 18.0 Hz, CH3), 14.3 (s, CH3), 22.8 (s, CH2),
22.9 (s, CH2), 26.6 (d, 2JC−P = 4.6 Hz, 3 × CH3), 27.0 (d, 2JC−P = 4.9
Hz, 3 × CH3), 27.1 (d, 2JC−P = 5.3 Hz, 3 × CH3), 27.5 (d, 2JC−P = 5.9
Hz, 3 × CH3), 29.5 (s, CH2), 29.7 (s, CH2), 29.8 (s, CH2), 30.0 (s,
3
3
9H), 0.92 (d, JH−P = 14.2 Hz, 9H), 1.13 (d, JH−P = 14.2 Hz, 9H),
2
2
1.86 (d, JH−P = 8.0 Hz, 3H), 1.93 (d, JH−P = 6.6 Hz, 3H), 5.72 (dd,
4JH−P = 7.2 Hz, J′H−P = 3.3 Hz, 1H), 7.90−7.83 (m, 2H), 8.23−8.14
4
3
1
CH2), 32.0 (d, JC−P = 3.9 Hz, CH2), 32.1 (s, CH2), 34.1 (d, JC−P
=
1
3
16.8 Hz, C), 34.8 (dd, JC−P = 22.6 Hz, J′C−P = 4.0 Hz, C), 35.2 (d,
1JC−P = 17.4 Hz, C), 36.1 (s, CH2), 72.7 (s, CH), 78.7 (s, CH), 130.0−
130.4 (m, 4 × CH), 131.3−131.7 (m, 4 × CH), 140.5 (s, C), 141.2 (s,
C), 141.6 (s, C), 205 (s, 4 × C). IR (ATR) ν (cm−1): 3050, 2958,
2923, 2860, 2026, 1958, 1540, 1505, 1473, 1195, 1144, 885, 761, 734.
HRMS (ESI): calcd for [C32H46Co2N2O4P2 + H+] 703.1670, found
703.1642.
(m, 2H). 31P{1H} NMR (162 MHz, CDCl3): δ (ppm) 54.16, 64.22.
13C NMR (100 MHz, CDCl3): δ (ppm) 2.8 (d, JC−P = 1.9 Hz, 3 ×
4
CH3), 11.9 (dd, 1JC−P = 21.5 Hz, 3J′C−P = 6.4 Hz, CH3), 12.0 (d, 1JC−P
= 15.4 Hz, CH3), 27.1 (d, 2JC−P = 4.6 Hz, 3 × CH3), 27.7 (d, JC−P
=
2
5.8 Hz, 3 × CH3), 34.3 (dd, 1JC−P = 19.3 Hz, 3J′C−P = 3.4 Hz, C), 35.3
(d, 1JC−P = 16.9 Hz, C), 85.9 (d, 3JC−P = 6.0 Hz, CH), 130.1 (d, 4JC−P
= 2.6 Hz, 2 × CH), 131.5 (d, 5JC−P = 6.1 Hz, 2 × CH), 140.8 (d, 3JC−P
= 7.0 Hz, C), 141.8 (d, 3JC−P = 5.7 Hz, C), 159.1 (dd, 1JC−P = 54.1 Hz,
2J′C−P = 45.6 Hz, C), 163.4 (dd, 1JC−P = 49.0 Hz, 2J′C−P = 35.0 Hz, C),
204.3−204.7 (m, 4 × C). IR (ATR) ν (cm−1): 3012, 2954, 2914, 2901,
2852, 2029, 1961, 1480, 1454, 1214, 750. HRMS (ESI): calcd for
[C27H38Co2N2O4P2Si + H+] 663.0813, found 663.0792.
(S,S)-QuinoxP*-Co2(CO)4-(μ-HCCPh) (3c). Phenylacetylene dicobalt
hexacarbonyl complex 2c (64 mg, 0.16 mmol, 1 equiv) was dissolved
in anhydrous toluene (2 mL). A solution of (S,S)-QuinoxP* (55 mg,
0.16 mmol, 1 equiv) in anhydrous toluene (2 mL) was then added
dropwise. The resulting mixture was stirred at 70 °C for 7 h. The
system was purged with a nitrogen flow every 30 min to remove the
CO. The crude mixture was filtered through an alumina plug, and the
product was purified by column chromatography in silica gel using
hexane/EtOAc (from 100/0 to 90/10) as the eluent to afford 3c (as a
3/1 mixture of diastereomers) (76 mg, 70% yield) as a dark red oil. 1H
General Procedure for the Pauson−Khand Reactions. In a
pressure glass tube equipped with a manometer, the corresponding
alkyne, norbornadiene, and the catalyst were dissolved in anhydrous
toluene under a nitrogen atmosphere. The system was purged with
nitrogen and then with carbon monoxide. Finally, the pressure of CO
was set to 1.5 BarG and the reaction mixture was heated to the
temperature indicated below for the appropriate time. The crude
reaction mixture was then filtered through an alumina plug, the solvent
was removed under reduced pressure, and the product was purified by
flash column chromatography on silica gel to afford the desired
compounds.
2-Octyl-3a,4,7,7a-tetrahydro-1H-4,7-methanoinden-1-one (4b).
1-Decyne (0.12 mL, 0.70 mmol, 1 equiv), norbornadiene (0.72 mL,
7 mmol, 10 equiv), and the catalyst 3c (34 mg, 0.05 mmol, 0.07 equiv)
were dissolved in anhydrous toluene (2.5 mL). The CO pressure was
set to 1.5 barG, and the mixture was stirred at 120 °C overnight. The
crude mixture was then filtered, and the product was purified by flash
3
NMR (400 MHz, CDCl3): δ (ppm) 0.71 (d, JH−P = 14.4 Hz, 9H),
3
3
0.82 (d, JH−P = 14.9 Hz, 9H*), 1.06 (d, JH−P = 13.8 Hz, 9H*), 1.17
(d, 3JH−P = 14.2 Hz, 9H), 1.52 (d, 2JH−P = 8.5 Hz, 3H*), 1.77 (d, 2JH−P
2
2
= 8.3 Hz, 3H), 1.92 (d, JH−P = 6.7 Hz, 3H), 2.06 (d, JH−P = 6.2 Hz,
3H*), 5.51 (d, 4JH−P = 12.1 Hz, 1H*), 5.66 (dd, 4JH−P = 8.5 Hz, 4J′H−P
= 1.8 Hz, 1H), 7.13−7.30 (m, 6H), 7.59−7.71 (m, 4H), 7.81−7.91 (m,
4H), 8.10−8.25 (m, 4H). 31P{1H} NMR (162 MHz, CDCl3): δ (ppm)
46.83, 53.59, 63.24, 64.76. 13C NMR (100 MHz, CDCl3): δ (ppm)
10.7−11.4 (m, 2 × CH3), 26.6 (d, 2JC−P = 4.8 Hz, 3 × CH3), 27.5 (d,
2JC−P = 5.9 Hz, 3 × CH3), 34.1 (d, 1JC−P = 17.7 Hz, C), 35.0 (d, 1JC−P
= 17.7 Hz), 72.4 (s, CH), 125.9 (s, CH), 128.1 (d, 4JC−P = 9.0 Hz, 2 ×
5
CH), 129.8−131.0 (m, 4 × CH), 131.5 (d, JC−P = 3.3 Hz, 2 × CH),
G
DOI: 10.1021/acs.organomet.7b00018
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
3
column chromatography on silica gel using hexane/EtOAc (from 100/
0 to 90/10) as the eluent to afford 4b (179 mg, 99% yield, 38% ee) as
5.6 Hz, J′H−H = 3.0 Hz, 1H), 7.59 (d, JH−H = 2.6 Hz, 1H). GC: β-
DEX (30 m), 160 °C, 1 mL/min, He. tR(−) = 18.0 min, tR(+) = 18.5
min.
a reddish oil. 1H NMR (400 MHz, CDCl3): δ (ppm) 0.88 (t, 3JH−H
=
7.0 Hz, 3H), 1.18−1.23 (m, 1H), 1.23−1.33 (m, 10H), 1.37 (dt, 2JH−H
2-(((tert-Butyldimethylsilyl)oxy)methyl)-3a,4,7,7a-tetrahydro-1H-
4,7-methanoinden-1-one (4f). tert-Butyldimethyl(prop-2-yn-1-
yloxy)silane (177 mg, 1.04 mmol, 1 equiv), norbornadiene (1.06
mL, 10.40 mmol, 10 equiv), and the catalyst 3a (43 mg, 0.07 mmol,
0.07 equiv) were dissolved in anhydrous toluene (3.5 mL). The CO
pressure was set to 1.5 barG, and the mixture was stirred at 100 °C for
6 h. The crude mixture was then filtered, and the product was purified
by flash column chromatography on silica gel using hexane/EtOAc
(from 100/0 to 90/10) as the eluent to afford 4f (260 mg, 86% yield,
= 9.3 Hz, 3J′H−H = 1.6 Hz, 1H), 1.41−1.51 (m, 2H), 2.15 (tdt, 3JH−H
=
4
4
3
7.3 Hz, J′H−H = 2.8 Hz, J″H−H = 1.5 Hz, 2H), 2.28 (dt, JH−H = 5.0
3
Hz, J′H−H = 1.4 Hz, 1H), 2.64−2.67 (m, 1H), 2.68−2.72 (m, 1H),
3
3
2.88−2.92 (m, 1H), 6.20 (dd, JH−H = 5.6 Hz, J′H−H = 3.0 Hz, 1H),
3
3
3
6.28 (dd, JH−H = 5.6 Hz, J′H−H = 3.0 Hz, 1H), 7.15 (dt, JH−H = 2.7
Hz, J′H−H = 1.4 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ (ppm)
4
14.2 (CH3), 22.8 (CH2), 25.1 (CH2), 27.9 (CH2), 29.4 (CH2), 29.5
(CH2), 29.6 (CH2), 32.0 (CH2), 41.3 (CH2), 43.1 (CH), 43.8 (CH),
47.8 (CH), 52.7 (CH), 137.2 (CH), 138.5 (CH), 151.0 (C), 158.8
(CH), 210.1 (C). IR (ATR) ν (cm−1): 3017, 2926, 2855, 1690, 1458,
1215, 747. HRMS (ESI): calcd for [C18H26O + H+] 259.2056, found
259.2058. GC: β-DEX (30 m), 180 °C, 1 mL/min, He. tR(−) = 63.0
min, tR(+) = 63.3 min.
1
8% ee) as a reddish oil. H NMR (400 MHz, CDCl3): δ (ppm) 0.06
2
(s, 6H), 0.90 (s, 9H), 1.21−1.26 (m, 1H), 1.38 (dt, JH−H = 9.3 Hz,
3J′H−H = 1.5 Hz, 1H), 2.32 (ddd, JH−H = 5.0 Hz, J′H−H = 1.6 Hz,
3
3
4J″H−H = 1.1 Hz, 1H), 2.67−2.71 (m, 1H), 2.72−2.77 (m, 1H), 2.83−
2.96 (m, 1H), 4.31−4.35 (m, 2H), 6.18 (dd, 3JH−H = 5.6 Hz, 3J′H−H
=
3
3
2-Phenyl-3a,4,7,7a-tetrahydro-1H-4,7-methanoinden-1-one (4c).
Phenylacetylene (90 μL, 0.82 mmol, 1 equiv), norbornadiene (0.59
mL, 5.70 mmol, 7 equiv) and the catalyst 3c (18 mg, 0.03 mmol, 0.03
equiv) were dissolved in anhydrous toluene (2 mL). The CO pressure
was set to 1.5 barG, and the mixture was stirred at 100 °C overnight.
The crude mixture was then filtered, and the product was purified by
flash column chromatography on silica gel using hexane/EtOAc (from
100/0 to 80/20) as the eluent to afford 4c (171 mg, 94% yield) as a
3.0 Hz, 1H), 6.27 (dd, JH−H = 5.6 Hz, J′H−H = 3.1 Hz, 1H), 7.35−
7.38 (m, 1H). 13C NMR (100 MHz, CDCl3): δ (ppm) −5.3 (2 ×
CH3), 18.5 (C), 26.0 (3 × CH3), 41.4 (CH2), 43.1 (CH), 43.7 (CH),
48.1 (CH), 53.7 (CH), 58.2 (CH2), 137.2 (CH), 138.6 (CH), 150.6
(C), 159.0 (CH), 208.7 (C). IR (ATR): ν (cm−1) 3012, 2945, 2923,
2852, 1687, 1215, 749. HRMS (ESI): calcd for [C17H26O2Si + H+]
291.1775, found 291.1779. HPLC: Chiralpak AS, heptane/IPA 98.5/
1.5, 0.5 mL/min, λ 210 nm. tR(R*) = 12.2 min, tR(S*) = 17.2 min.
1-Oxo-3a,4,7,7a-tetrahydro-1H-4,7-methanoinden-2-yl)methyl
Acetate (4g). Propargyl acetate (66 μL, 0.66 mmol, 1 equiv),
norbornadiene (0.68 mL, 6.6 mmol, 10 equiv), and the catalyst 3c (22
mg, 0.03 mmol, 0.05 equiv) were dissolved in anhydrous toluene (2
mL). The CO pressure was set to 1.5 barG, and the mixture was
stirred at 100 °C overnight. The crude mixture was then filtered, and
the product was purified by flash column chromatography on silica gel
using hexane/EtOAc (from 100/0 to 70/30) as the eluent to afford 4g
1
pale brown solid. H NMR (400 MHz, CDCl3): δ (ppm) 1.34 (dt,
2JH−H = 9.4 Hz, 3J′H−H = 1.5 Hz, 1H), 1.43 (dt, 2JH−H = 9.4 Hz, 3J′H−H
3
= 1.6 Hz, 1H), 2.47 (dt, JH−H = 5.2 Hz, 3J′H−H = 1.4 Hz, 1H), 2.76−
2.80 (m, 1H), 2.82−2.86 (m, 1H), 2.99−3.05 (m, 1H), 6.25 (dd, 3JH−H
= 5.6 Hz, 3J′H−H = 3.0 Hz, 1H), 6.33 (dd, 3JH−H = 5.6 Hz, 3J′H−H = 3.1
Hz, 1H), 7.29−7.40 (m, 3H), 7.67−7.72 (m, 3H). 13C NMR (100
MHz, CDCl3): δ (ppm) 41.5 (CH2), 43.5 (CH), 44.3 (CH), 47.3
(CH), 53.7 (CH), 127.2 (2 × CH), 128.5 (2 × CH), 128.6 (CH)
131.8 (C), 137.3 (CH), 138.7 (CH), 147.3 (C), 160.0 (CH), 207.8
(C). IR (ATR): ν (cm−1) 3060, 3015, 2974, 2939, 2876, 1694, 1493,
1323, 1215, 1142, 751. HRMS (ESI): calcd for [C16H14O + H+]
223.1117, found 223.1122. HPLC: Chiralcel OD-H, heptane/IPA 98/
2, 1.0 mL/min, λ 254 nm. tR(+) = 12.1 min, tR(−) = 15.8 min.
2-(2-Hydroxypropan-2-yl)-3a,4,7,7a-tetrahydro-1H-4,7-metha-
noinden-1-one (4d). 2-Methylbut-3-yn-2-ol (64 μL, 0.66 mmol, 1
equiv), norbornadiene (0.68 mL, 6.6 mmol, 10 equiv), and the catalyst
3c (22 mg, 0.03 mmol, 0.05 equiv) were dissolved in anhydrous
toluene (2 mL). The CO pressure was set to 1.5 barG, and the mixture
was stirred at 110 °C overnight. The crude mixture was then filtered,
and the product was purified by flash column chromatography on silica
gel using hexane/EtOAc (from 100/0 to 40/60) as the eluent to afford
1
(57 mg, 40% yield, 5% ee) as a yellow oil. H NMR (400 MHz,
CDCl3): δ (ppm) 1.21−1.26 (m, 1H), 1.39−1.44 (m, 1H), 2.09 (s,
3H), 2.34−2.37 (m, 1H), 2.71−2.74 (m, 1H), 2.78−2.82 (m, 1H),
2.95 (s, 1H), 4.74 (s, 2H), 6.22 (dd, 3JH−H = 5.6 Hz, 3J′H−H = 3.0 Hz,
3
3
1H), 6.30 (dd, JH−H = 5.7 Hz, J′H−H = 3.2 Hz, 1H), 7.41−7.44 (m,
1H). 13C NMR (100 MHz, CDCl3): δ (ppm) 21.0 (CH3), 41.4
(CH2), 43.1 (CH), 43.9 (CH), 48.3 (CH), 53.1 (CH), 58.1 (CH2),
137.3 (CH), 138.6 (CH), 145.2 (C), 162.0 (CH), 170.8 (C), 207.9
(C). IR (ATR): ν (cm−1) 3056, 2974, 2939, 2876, 2848, 1742, 1698,
1367, 1227, 1027, 706. HRMS (ESI): calcd for [C13H14O3 + H+]:
219.1016, found 219.1020. GC: β-DEX (30 m), 150 °C, 1 mL/min,
He. tR(R*) = 37.5 min, tR(S*) = 37.6 min.
2-(1-Hydroxyethyl)-3a,4,7,7a-tetrahydro-1H-4,7-methanoinden-
1-one (4h). But-3-yn-2-ol (35 μL, 0.43 mmol, 1 equiv), norbornadiene
(0.45 mL, 4.3 mmol, 10 equiv), and the catalyst 3c (20 mg, 0.03 mmol,
0.07 equiv) were dissolved in anhydrous toluene (2 mL). The CO
pressure was set to 1.5 barG, and the mixture was stirred at 100 °C
overnight. The crude mixture was then filtered, and the product was
purified by flash column chromatography on silica gel using hexane/
EtOAc (from 100/0 to 20/80) as the eluent to afford 4h (as a ca. 2/1
mixture of diastereomers) (18 mg, 22% yield, 30% ee) as a yellow oil.
1H NMR (400 MHz, CDCl3): δ (ppm) 1.25−1.29 (m, 1H), 1.40 (d,
1
4d (22 mg, 16% yield, 25% ee) as a yellow oil. H NMR (400 MHz,
CDCl3): δ (ppm) 1.22−1.26 (m, 1H), 1.38−1.42 (m, 1H), 1.43 (s,
3
6H), 2.33 (d, JH−H = 5.1 Hz, 1H), 2.68−2.77 (m, 2H), 2.93 (s, 1H),
3
3
3.68 (br s, 1H), 6.22 (dd, JH−H = 5.6 Hz, J′H−H = 3.0 Hz, 1H), 6.31
3
3
3
(dd, JH−H = 5.6 Hz, J′H−H = 3.1 Hz, 1H), 7.25 (d, JH−H = 2.7 Hz,
1H). 13C NMR (100 MHz, CDCl3): δ (ppm) 28.6 (CH3), 29.1
(CH3), 41.2 (CH2), 43.1 (CH), 43.9 (CH), 47.2 (CH), 53.5 (CH),
69.9 (C), 137.2 (CH), 138.7 (CH), 155.3 (C), 157.2 (CH), 210.5
(C). IR (ATR): ν (cm−1) 3446, 3060, 3009, 2978, 2939, 2870, 1682,
1315, 750. HRMS (ESI): calcd for [C13H16O2 + H+] 205.1223, found
205.1219. HPLC: Chiralcel OD-H, heptane/IPA 95/5, 1.0 mL/min, λ
220 nm. tR(−) = 8.6 min, tR(+) = 10.1 min.
3JH−H = 6.5 Hz, 3H), 1.39−1.43 (m, 1H), 2.34 (dt, JH−H = 4.9 Hz,
3
3J′H−H = 1.4 Hz, 1H), 2.69−2.73 (m, 1H), 2.75−2.79 (m, 1H), 2.93 (s,
2H), 4.60 (q, 3JH−H = 6.8 Hz, 1H), 6.22 (dd, 3JH−H = 5.6 Hz, 3J′H−H
=
2-(Trimethylsilyl)-3a,4,7,7a-tetrahydro-1H-4,7-methanoinden-1-
one (4e). Trimethylsilylacetylene dicobalt hexacarbonyl complex 2e
(100 mg, 0.26 mmol, 1 equiv) was dissolved in anhydrous toluene (7
mL). Norbornadiene (0.27 mL, 2.6 mmol, 10 equiv) was then added,
and the solution was stirred at 70 °C for 2 h. The crude mixture was
then filtered, and the product was purified by flash column
chromatography on silica gel using hexane/ethyl acetate (from 100/
0 to 80/20) as the eluent to afford 4e (14 mg, 25% yield) as a white
solid.27 1H NMR (400 MHz, CDCl3): δ (ppm) 0.19 (s, 9H), 1.19 (d,
3
3
3.0 Hz, 1H), 6.31 (dd, JH−H = 5.6 Hz, J′H−H = 3.1 Hz, 1H), 7.29−
7.33 (m, 1H). 13C NMR (100 MHz, CDCl3): δ (ppm) 21.72
(CH3 diast 2), 21.80 (CH3 diast 1), 41.24 (CH2 diast 2), 41.27 (CH2 diast 1),
43.02 (CHdiast 2), 43.05 (CHdiast 1), 43.76 (CHdiast 2), 43.78 (CHdiast 1),
47.85 (CHdiast 2), 47.87 (CHdiast 1), 53.44 (CHdiast 2), 53.51 (CHdiast 1),
63.77 (CHdiast 2), 63.92 (CHdiast 1), 137.19 (CHdiast 2), 137.21
(CHdiast 1), 138.65 (CHdiast 2), 138.70 (CHdiast 1), 152.97 (Cdiast 1),
153.07 (Cdiast 2), 158.22 (CHdiast 1), 158.26 (CHdiast 2), 210.13 (Cdiast 2),
210.26 (Cdiast 1). IR (ATR): ν (cm−1) 3414, 3063, 2974, 2933, 2876,
1683, 1626, 1215, 749. HRMS (ESI): calcd for [C12H14O2 + H+]
191.1067, found 191.1066. HPLC: Chiralpak IA, heptane/EtOH 90/
3
2JH−H = 9.3 Hz, 1H), 1.35−1.40 (m, 1H), 2.29 (dt, JH−H = 5.2 Hz,
3J′H−H = 1.4 Hz, 1H), 2.69 (br s, 1H), 2.82−2.86 (m, 1H), 2.91 (br s,
1H), 6.20 (dd, 3JH−H = 5.6 Hz, 3J′H−H = 3.0 Hz, 1H), 6.27 (dd, 3JH−H
=
H
DOI: 10.1021/acs.organomet.7b00018
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
10, 1.0 mL/min, λ 210 nm. tR(R* diast 1) = 9.9 min, tR(R* diast 2) =
13.9 min, tR(S* diast 1) = 19.5, tR(S* diast 2) = 20.6 min.
ACKNOWLEDGMENTS
■
We thank the Spanish Ministerio de Economia y Competividad
(CTQ2014-56361-P) and IRB Barcelona for financial support.
IRB Barcelona is the recipient of a Severo Ochoa Award of
Excellence from MINECO (Government of Spain). Dr. Carme
Rovira is gratefully acknowledged for the CPU time.
2-Cyclopropyl-3a,4,7,7a-tetrahydro-1H-4,7-methanoinden-1-one
(4i). Cyclopropylacetylene (72 μL, 0.85 mmol, 1 equiv), norborna-
diene (0.88 mL, 8.5 mmol, 10 equiv), and the catalyst 3a (25 mg, 0.04
mmol, 0.05 equiv) were dissolved in anhydrous toluene (2.5 mL). The
CO pressure was set to 1.5 barG, and the mixture was stirred at 110 °C
overnight. The crude mixture was then filtered, and the product was
purified by flash column chromatography on silica gel using hexane/
EtOAc (from 100/0 to 80/20) as the eluent to afford 4i (157 mg, 99%
yield, 43% ee) as a yellow oil. 1H NMR (400 MHz, CDCl3): δ (ppm)
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0.58−0.64 (m, 2H), 0.80−0.86 (m, 2H), 1.20 (dt, JH−H = 9.3 Hz,
3J′H−H = 1.6 Hz, 1H), 1.36 (dt, 2JH−H = 9.3 Hz, 3J′H−H = 1.6 Hz, 1H),
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(s, 1H), 6.19 (dd, JH−H = 5.6 Hz, J′H−H = 3.0 Hz, 1H), 6.26 (dd,
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3
3
13C NMR (100 MHz, CDCl3): δ (ppm) 6.5 (CH), 7.6 (CH2), 7.8
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(0.49 mL, 4.70 mmol, 10 equiv), and the catalyst 3c (22 mg, 0.03
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00018.
■
S
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AUTHOR INFORMATION
Corresponding Authors
*E-mail for X.V.: xavier.verdaguer@irbbarcelona.org.
*E-mail for A.R.: antoni.riera@irbbarcelona.org.
ORCID
Xavier Verdaguer: 0000-0002-9229-969X
Antoni Riera: 0000-0001-7142-7675
Notes
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The authors declare no competing financial interest.
I
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